THE EFFECT OF SINTERING PROCESS ON THE SUPERCONDUCTING PROPERTIES OF MgB_2 BULK AND TAPE

摘要

MgB_2 superconductor with critical transition temperature of 39.9K has been synthesized. The supercoducting properties of MgB_2 bulk have been also studied after re-sintering heat treatment at 600℃, 700℃ and 800℃, It is found that the critical transition temperatures (onset) have slightly difference among the three samples. However, the transition widths and the normal state resistivity at 40K increase dramatically with increasing the re-sintering temperature for the 700℃ and 800℃ samples, corresponding to the occurrence of more impurities confirmed by x-ray diffraction patterns. At the same time, the microstructure shows that the grain size of MgB_2 grows larger and the structure becomes even dense. The transport critical current density for the unsintered Ni sheathed MgB_2 tape reaches 3.8x10~3A/cm~2, while the superconducting properties are very poor for the MgB_2 tapes subjected re-sintering process. This can be interpreted by forming more impurities during re-sintering process due to some air sealed into the tube during PIT process.